It's a common issue. You can check below steps to fix it.
How to Make iTunes Recognize iPhone
There are many reasons why iTunes will not recognize your iPhone or iPad, whether it's dust or dirt blocking your dock connector or a system setting gone wrong. No matter what model iPhone or iPad you have, here are a few suggestions for helping the problem of iTunes not recognizing iPhone:
1. Generally speaking, when iTunes does not recognize iPhone, it may have something to do with the version of iTunes. If you are using an old version of iTunes on your computer, it may not be capable of recognizing your iOS devices. So updating iTunes to the latest version is a fastest way to get the problem solved.
2. If you are running iTunes in the latest version, but still can't get your iPhone recognized, you may want to take a look at your computer, sometimes if your computer lacks necessary software, it might lead to the malfunction of iTunes.
3. USB port on your computer can be another reason why iPhone not recognized by iTunes. So you can try more than one USB port to see whether the USB port works well.
4. Of course, your iPhone may also be the cause of iTunes not recognizing iPhone. At this moment, you can restart your iPhone by holding the Sleep/Wake button and Home button at the same time until you see the Apple logo, then connect iPhone to computer with USB cable again.
5. You should also make sure your iPhone trusts your computer, because after changing a new system on computer, your iPhone will regard it as a new computer. What's more, you should check out whether Apple Mobile Device Support is installed on computer.
6. After checking out all the aspects mentioned above, you can try to connect iPhone to computer with the USB cable again.
If none of these methods work out, you may want to try set your iPhone up as new after iTunes not recognizing iPhone
. You only need to tap General > Settings > Reset > Erase All Content and Settings, and then choose Set Up as New. When you have set iPhone up as a new device, you are able to connect iPhone to computer with USB cable. But before erasing all contents on your iPhone, you may want to back up iPhone files to computer to keep them safe.
For more details,check: What to Do When iTunes Not Recognizing iPhone